This invention relates to automatic testing systems for use in the automatic diagnoses of faults in electronic circuits such as printed circuit boards bearing electrical components, either following manufacture or following service during which faults have developed.
One example of an automatic test apparatus of the above kind is illustrated in FIG. 1 of the accompanying drawings which is a block schematic diagram.
Referring to FIG. 1, a printed circuit board having mounted thereon electrical components (which are not separately shown) and to be tested is represented at 1. Provided to carry out an automatic test of the printed circuit board is an automatic test apparatus 2 which is in fact a proprietary machine marketed by Marconi Instruments Limited under the trade name "Autotest System 80". It will not be necessary to describe the automatic testing machine in detail but in essence it is mechanically similar to the machine described in the specification of our U.K. Pat. No. 1,530,350. Provision is made to monitor voltage levels at a plurality of different points in the circuit of the printed circuit board 1 and from these readings and from stored information relating to the different voltages values to be expected of a satisfactory board and factors which would be responsible for variations therein, signals are produced which are displayed upon a visual display unit 3 which in this case again is an instrument marketed by Marconi Instruments under the Type Number TK1864. The visual display unit 3 will in operation display such information as "R 14 1.02K H" or "short 100 101". This information conveys to the operator that resistor R14 in the circuit has a value of 1.02K.OMEGA. which is high or above tolerance and that a short circuit is apparent at a position identified by the positional reference numbers 100 and 101. Whilst examples of only two faults are given, obviously in any given case a greater number of faults may be displayed on the visual display unit 3.
The operator may then enter, by means of the keyboard of the visual display unit 3, the serial number of the printed circuit board 1 under test and obtain a print-out showing all of the faults diagnosed in that particular printed circuit board.
In order to avoid the necessity of the operator having to read and enter the serial number of the printed circuit board 1 under test the serial number (represented at 4) may be provided not only in conventional numeric form but also in the form of bar code which is read by an optical reader 5. The block 6 represents a suitable interface e.g. a Type 9300 interface manufactured by Interface Mechanisms Inc of USA.
As so far described the system constitutes an automatic test system which is as well known per se. Such a system is capable of performing automatic tests at a relatively high rate and in practice it is difficult to provide a repair facility which is capable of keeping up with the correction of faults diagnosed by the apparatus.